Influence of temperature on the inactivation kinetics of Salmonella Enteritidis by the application of UV-C technology in soymilk

Abstract

The Ultraviolet-C technology is proposed as an alternative to thermal pasteurization for decontamination of soymilk, as heat treatments may adversely affect its quality. The aim of this study was to evaluate and model the influence of different processing temperatures (4–30 °C) on the inactivation of Salmonella Enteritidis in soymilk at different UV-C doses. Inactivation efficiency was potentiated by the increase in temperature from 4 to 18 °C. Higher temperatures (ranging from 18 to 30 °C) did not yield significant differences between Salmonella maximum inactivation levels, i.e. difference between concentrations after and before treatments. The Weibull model was suitable to describe the inactivation data as a function of UV-C dose, at all temperatures evaluated. Since the Weibull shape parameter (p) was statistically homogeneous at temperatures ranging from 8 to 30 °C (P > 0.05), it was fixed at its mean value (0.68 ± 0.08) and inactivation curves were re-fitted. Secondary modelling was conducted only to establish a relationship between Weibull model scale parameter (δ) and temperature. The δ estimations indicate that lower UV-C doses are required at 18–30 °C to attain a first tenfold reduction of Salmonella population in soymilk. Finally, a model combining primary and secondary models was developed to predict Salmonella inactivation at different UV-C doses and temperatures. This model provided acceptable predictions of inactivation data at temperatures within its limits. Accurate predictions of microbial inactivation curves at different combinations of UV-C doses and processing temperatures would be beneficial in setting favourable conditions of UV-C application to achieve desired levels of bacterial inactivation in soymilk.